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Old 12-05-2017, 05:43 PM   #1
Blacktek
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Default Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

hi guys, this macbook it was working fine til i replaced the keyboard, after i put it back together it started beeping 3 times, and no video, it goes on endlessly.

Schematic and boardview attached.

C7332 is getting 12.5v, but nothing coming out of Q7330.. please help.
Attached Files
File Type: pdf a1278 J30 820-3115-B 051-9058.pdf (1.49 MB, 27 views)
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Old 12-06-2017, 04:08 AM   #2
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

3 beep means memory ram. remove and put one ram module at once.
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Old 12-06-2017, 11:22 AM   #3
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

i did, multiple times, tried different memories even, but still beeping
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Old 12-06-2017, 01:53 PM   #4
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

remove q7330 and report voltage on pin 1-2-3-4-5
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Old 12-06-2017, 02:17 PM   #5
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
remove q7330 and report voltage on pin 1-2-3-4-5
removed mosfet: pins 1-4 0volts, pin 5 has 12.5 V

I've been tracing rails that produce 1.5v and notice that R2801 Has 3.3 on 1 side and 0 volts on the other side, it has the correct value which is 100k.
.
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Old 12-06-2017, 03:29 PM   #6
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

u7300 voltages ?
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Old 12-06-2017, 04:38 PM   #7
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
u7300 voltages ?
pin 1-5= 0.0v
pin 6= 1.8v
pin 7= 0.0v
pin 8 = 1.5v
pin 9-10= 0.0v
pin 11= 0.080v
pin 12= 5.0v
pin 13-14= 1.5v
pin 15= 6.5
pin 16-17= 3.3v
pin 18= 0.70v
pin 19= 0.0v
pin 20=0.080v
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Old 12-06-2017, 04:48 PM   #8
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

check if pin 4 and 5 of q7335 is shorted, if yes replace q7335

if pin 4-5 no shorted replace u7300

edit: voltage on l7330 without any ram module ?

Last edited by dellxps15; 12-06-2017 at 04:53 PM..
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Old 12-06-2017, 05:19 PM   #9
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
check if pin 4 and 5 of q7335 is shorted, if yes replace q7335

if pin 4-5 no shorted replace u7300

edit: voltage on l7330 without any ram module ?
Q7335 not shorted.
Measurement of u7300 where without ram.
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Old 12-06-2017, 05:28 PM   #10
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

ok then try to replace u7300
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Old 12-06-2017, 05:39 PM   #11
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
ok then try to replace u7300
ok thanks friend i'll try to find another one of these bad boys.
is this chip responsible for creating 1.5v?

is it safe to make a jumper from pin 8 on u7300 to q7335?

Last edited by Blacktek; 12-06-2017 at 05:48 PM..
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Old 12-06-2017, 06:19 PM   #12
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

wait: pin 4 of q7330 (after removed) has 0 volt, but pin 14 has 1.5 volt.... check c7325

if u can try this first before replacing u7300.

no dont do that jumper wire.

u7300 got enable signal from pin 16, but power good is not ok.

this chip create 1.5 volt for ram memory.

ps: pin 4 of q7330 has 0 volt after u removed it ?

Last edited by dellxps15; 12-06-2017 at 06:20 PM..
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Old 12-07-2017, 05:33 PM   #13
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
wait: pin 4 of q7330 (after removed) has 0 volt, but pin 14 has 1.5 volt.... check c7325

if u can try this first before replacing u7300.

no dont do that jumper wire.

u7300 got enable signal from pin 16, but power good is not ok.

this chip create 1.5 volt for ram memory.

ps: pin 4 of q7330 has 0 volt after u removed it ?
C7325 is ok, not shorted.

Q7330 has 12.5v on pin 5, Pins 1-4 has 0v, whether is on or off the board.

I noticed resistor 2801 has 3.3v on 1 side and 0v on the other side, which is supposed to be 1.5v..Does this has anything to do with the memory not being recognized?
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Old 12-08-2017, 04:45 AM   #14
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

circuit about r2801 also generate ddrvtt_en that is present on pin 17 of q7330

edit: volt on R2810 both side.

is pch getting extremely hot ? if yes could also be a bad nb chip.

Last edited by dellxps15; 12-08-2017 at 04:54 AM..
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Old 12-08-2017, 05:41 PM   #15
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Default Re: Macoook Pro A1278 3 Beeps, Missing 1.5v rail voltage please help 820-3115-B..

Quote:
Originally Posted by dellxps15 View Post
circuit about r2801 also generate ddrvtt_en that is present on pin 17 of q7330

edit: volt on R2810 both side.

is pch getting extremely hot ? if yes could also be a bad nb chip.
Nothing is getting overheated. R2810 has 3.3 on 1 side and 0.0v on the other side.
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